1. Field of the Invention
The present invention relates to a roll-off reducing agent in the polishing step and a polishing composition using the roll-off reducing agent. Furthermore, the present invention relates to a process for producing a substrate comprising applying the polishing composition to the substrate, and a process for reducing roll-off in the polishing step comprising applying the polishing composition to a substrate.
2. Discussion of the Related Art
Over the years, a demand for a technique for further increasing the capacity of the hard discs has become greater. As a leading means for increasing the capacity of the hard discs, there has been considered a means of producing a substrate capable of recording data even to its outer periphery by reducing roll-off (edge rounding of end side of a substrate) caused in the polishing process. For instance, various mechanical polishing conditions, such as making a polishing pad more rigid, and making a polishing load smaller, have been studied in order to produce a substrate having a reduced roll-off. However, although a certain extent of an effect is obtained by reducing roll-off with these mechanical polishing conditions, the effect has not yet been satisfactory. Also, from the viewpoint of reducing roll-off from the polishing composition used in the polishing step, the use of a specified organic acid represented by an organic acid having hydroxyl group (Japanese Patent Laid-Open No. 2002-12857), the use of sol product of aluminum salt (Japanese Patent Laid-Open No. 2002-20732) and the like have been proposed. However, roll-off cannot be said to be satisfactorily reduced.
As mentioned above, the reason why the roll-off is generated in the end side portion of the substrate at which the surface is more polished than that the internal of the substrate is presumably due to the fact that the pressure during polishing of the substrate is higher at the end side portion than that of the internal of the substrate. Therefore, the present inventors have remarked on a compound capable of controlling aggregation of abrasive grains of the abrasive from a new viewpoint not found conventionally in which the difference in pressure is caused by polishing the end side portion undesirably greatly when the abrasive comes between the substrate and the polishing device such as a polishing pad, due to the fact that an aggregation force of the abrasive grains of the abrasive is large. The present invention has been perfected thereby.